std::generate_canonical

Defined in header `<random>`
template< class RealType, std::size_t Bits, class Generator > RealType generate_canonical( Generator& g );		(since C++11)

Generates a random floating point number in range $\small [0,1)$ $[0, 1)$ .

To generate enough entropy, generate_canonical() will call g() exactly $\small k$ $k$ times, where $k = max(1, ⌈ b / log 2 R ⌉)$ and

b = std::min(Bits, std::size_t{std::numeric_limits<RealType>::digits}),
R = g.max() - g.min() + 1.

Parameters

g

-

generator to use to acquire entropy

Return value

Floating point value in range $\small [0,1)$ $[0, 1)$ .

Exceptions

None except from those thrown by g

Notes

Some existing implementations have a bug where they may occasionally return 1.0 if RealType is float GCC #63176 LLVM #18767 MSVC STL #1074. This is LWG issue 2524.

Example

produce random numbers with 10 bits of randomness: this may produce only k*R distinct values

Run this code

#include <random>
#include <iostream>
 
int main()
{
    std::random_device rd;
    std::mt19937 gen(rd());
    for(int n=0; n<10; ++n) {
        std::cout << std::generate_canonical<double, 10>(gen) << ' ';
    }
}

Possible output:

0.208143 0.824147 0.0278604 0.343183 0.0173263 0.864057 0.647037 0.539467 0.0583497 0.609219

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